The individual and combined effects of X-irradiation and hyperthermia on early somite mouse embryos in culture.

The effects of 1) X-irradiation and 2) hyperthermia at a temperature of 43 degrees C individually and in combination have been investigated using cultured 8-day mouse embryos. B6C3F1 embryos were exposed to 0.3-2.0 Gy of X-rays, 5-20 min of heating, or 5 min of heating and irradiation at 0.3, 0.6, and 0.9 Gy. Irradiation alone at 0.3 Gy showed no apparent effect on embryonic development, but irradiation at 0.6-2.0 Gy caused a dose-dependent increase in malformed embryos. Heating alone for 5 min produced no malformed embryos, while heating for 10-20 min caused malformations as a function of heating time. Combined treatments produced higher frequencies (22.2-100%) of malformations than those of the sum of the separate treatments (0-41.7%). Malformations observed were primarily microphthalmia, microcephaly, and open neural tubes. The results indicate that in cultured mouse embryos irradiation combined with a "nonteratogenic dose" of hyperthermia directly exerts an additive effect on formation of the malformed embryos. In addition, a single occurrence of left-sided tail was produced by hyperthermia alone, while four occurrences were produced in combination with radiation.     

Lung tumour induction in mice after X-rays and neutrons

Dose-response curves were determined for pulmonary adenomas and adenocarcinomas in mice after single acute doses of 200 kVp X-rays and cyclotron neutrons (E = 7.5 MeV). A serial-killing experiment established that the radiation induces the tumours and does not merely accelerate the appearance of spontanoeus cancers [corrected]. The dose versus incidence (I) of tumours in male and female mice for X-ray doses between 0.25 and 7.5 Gy is 'bell-shaped' and best fitted with a purely quadratic induction and exponential inactivation terms, i.e. I = A + BD2e-alpha D. In contrast, the tumour dose-response after 0.1-4.0 Gy of neutrons is best fitted by I = A + BDe-alpha D and is steeply linear less than or equal to 1 Gy, peaks between 1 and 3 Gy and sharply declines at 4.0 Gy. The data for the female mice less than or equal to 1 Gy neutrons are best fitted to the square root of the dose. A major objective of the experiments was to derive neutron RBE values. Because of the differences between the X-ray (quadratic) and neutron (linear) curves, the RBEn will vary inversely with decreasing X-ray dose. The RBE values at 1 Gy of X-rays derived from the B coefficients in the above equations are 7.4 +/- 3.2 (male and female); 8.6 +/- 3.6 (female) and 4.7 +/- 1.8 (male). These are high values and imply even higher values at the doses of interest to radiation protection. If, however, one restricts the analysis to the initial, induction side of the response (less than or equal to 1 Gy neutrons, less than or equal to 3 Gy X-rays) then good linear fits are obtainable for both radiations and indicate neutron RBE values of 7.4 +/- 2.3 for female mice and 4.5 +/- 1.8 for males, and these are independent of dose level.     

Implication of prostaglandins and histamine H1 and H2 receptors in radiation-induced temperature responses of rats

Exposure of rats to 1-15 Gy gamma radiation (60Co) induced hyperthermia, whereas 20-200 Gy induced hypothermia. Exposure either to the head or to the whole body to 10 Gy induced hyperthermia, while body-only exposure produced hypothermia. This observation indicates that radiation-induced fever is a result of a direct effect on the brain. The hyperthermia due to 10 Gy was significantly attenuated by the pre- or post-treatment with a cyclooxygenase inhibitor, indomethacin. Hyperthermia was also altered by the central administration of a mu-receptor antagonist naloxone but only at low doses of radiation. These findings suggest that radiation-induced hyperthermia may be mediated through the synthesis and release of prostaglandins in the brain and to a lesser extent to the release of endogenous opioid peptides. The release of histamine acting on H1 and H2 receptors may be involved in radiation-induced hypothermia, since both the H1 receptor antagonist, mepyramine, and H2 receptor antagonist, cimetidine, antagonized the hypothermia. The results of these studies suggest that the release of neurohumoral substances induced by exposure to ionizing radiation is dose dependent and has different consequences on physiological processes such as the regulation of body temperature. Furthermore, the antagonism of radiation-induced hyperthermia by indomethacin may have potential therapeutic implications in the treatment of fever resulting from accidental irradiations.     

Relative cataractogenic effects of X rays, fission-spectrum neutrons, and 56Fe particles: a comparison with mitotic effects

The eyes of Sprague-Dawley rats were irradiated with doses of 2.5-10 Gy 250-kVp X rays, 1.25-2.25 Gy fission-spectrum neutrons (approximately 0.85 MeV), or 0.1-2.0 Gy 600-MeV/A 56Fe particles. Lens opacifications were evaluated for 51-61 weeks following X and neutron irradiations and for 87 weeks following X and 56Fe-particle irradiations. Average stage of opacification was determined relative to time after irradiation, and the time required for 50% of the irradiated lenses to achieve various stages (T50) was determined as a function of radiation dose. Data from two experiments were combined in dose-effect curves as T50 experimental values taken as percentages of the respective T50 control values (T50-% control). Simple exponential curves best describe dose responsiveness for both high-LET radiations. For X rays, a shallow dose-effect relationship (shoulder) up to 4.5 Gy was followed at higher doses by a steeper exponential dose-effect relationship. As a consequence, RBE values for the high-LET radiations are dose dependent. Dose-effect curves for cataracts were compared to those for mitotic abnormalities observed when quiescent lens epithelial cells were stimulated mechanically to proliferate at various intervals after irradiation. Neutrons were about 1.6-1.8 times more effective than 56Fe particles for inducing both cataracts and mitotic abnormalities. For stage 1 and 2 cataracts, the X-ray Dq was 10-fold greater and the D0 was similar to those for mitotic abnormalities initially expressed after irradiation.     

Radiation quality and rat motor performance

The effects of bremsstrahlung, electron, gamma, and neutron radiations were investigated on the motor performance of male Sprague-Dawley rats. Rats were irradiated at a midline tissue dose rate of 20 Gy/min +/- 1 with one of the following: 18.6-MeV electrons (N = 40) or 18.1-MVp bremsstrahlung (N = 57) from a linear accelerator, 60Co 1.25-MeV gamma-ray photons (N = 48), or reactor neutrons at 1.67 MeV tissue-kerma weighted-mean energy (N = 43). Radiation effects were determined by establishing median effective doses (ED50) for rats trained on an accelerod, a shock-avoidance motor performance test. ED50's were based on 10-min postexposure performance. The ED50's were 61 Gy for electrons, 81 Gy for bremsstrahlung, 89 Gy for gamma-ray photons, and 98 Gy for neutrons. In terms of relative biological effectiveness to produce early performance decrement (10 min from the start of irradiation), significant differences existed between the electrons and the other three fields and between the bremsstrahlung and neutron fields. These differences could not be explained by macroscopic dose distribution patterns in the irradiated animals. The data imply that different radiation qualities are not equally effective at disrupting performance, with high-energy electrons being the most effective and neutrons the least.     

Action of hyperthermia on the early radiation reactions of HeLa cells in a stationary growth stage

A study was made of the influence of hyperthermia (42 degrees C, 30 min) after irradiation with a dose of 6 Gy on the permeability of cell membranes and the rate of incorporation of 3H-thymidine into DNA of HeLa cells at the stationary stage of the culture growth. Hyperthermia was shown to enhance the damaging effect of radiation on cells at this growth stage. It is suggested that this effect is connected with the impaired development of a series of early (during the first minutes and hours) adaptive reactions of HeLa cells, at the stationary stage of growth, to the effect of radiation.     

Combined Effect of Neutron and Proton Radiations on the Growth of Solid Ehrlich Ascites Carcinoma and Remote Effects in Mice

Doklady Biochemistry and Biophysics - The combined effect of the irradiation with a proton pencil scanning beam (PBS) at a total dose of 80 Gy and neutron radiation at a dose of 5 Gy on the growth...     

Modification of the effects of hyperthermia and neutron radiation on the activity of acid phosphatase in CaNT tumors.

Acid phosphatase activity was measured in implanted murine CaNT tumors of varying volumes. There is a clear monotonically increasing relation between acid phosphatase activity and tumor volume. Also the tumors were subjected to either induced artificial hypoxia or hyperthermia (41.0 degrees C) alone, or combined with neutron irradiation (3.8 Gy). Changes in the activity of this enzyme following radiation damage could reflect tissue damage associated with metabolic disturbances. The effect on enzyme activity after sequential hyperthermia and neutron irradiation is not synergistic, as is shown in the quantitative experimental data. This implies that the mechanisms of heat damage differ from that of neutron beam damage, as reflected by acid phosphatase activity. The CaNT tumor was also shown to be thermosensitive after administration of mitoxantrone. Finally, the role of exogenous ATP was shown to provide heat protection by modification of those thermal effects resulting in the activity of acid phosphatase. The augmentation of this hydrolytic enzyme probably represents initial metabolic damage in the tumor after different modalities of radiation alone, or combined with mitoxantrone and exogenous ATP.     

Normal killer function in CBA mice as affected by long-term intake of tritium oxide

A study was made of the cytotoxic function of normal killers of CBA mice during long-term administration of tritium oxide in potable water (a cumulative absorbed dose of 8.7 Gy, dose-rate, 4.5 Gy/day) and at different times after termination of the radionuclide injection. A mean decrease of 20-30% in the lytic effect of the effectors from spleen of the experimental mice on cell-targets of K-562 human erythroleukosis was demonstrated by a 17-19-hour test with 51Cr. At later times after termination of action of tritium oxide, the cytotoxic effect of normal killers increased by 1.8 times as compared to intact controls of the same age.     

Relative biological effectiveness (RBE) of thermal neutron capture therapy of cultured B-16 melanoma cells preincubated with 10B-paraboronophenylalanine

An experimental study of the relative biological effectiveness (RBE) of thermal neutron capture therapy (TNCT) for melanoma cell inactivation using 10B1-paraboronophenylalanine (10B1-BPA) was carried out to demonstrate a high therapeutic effect of TNCT, compared with that of fast neutron. Cells preincubated with or without 10B1-BPA at a concentration of 50 micrograms/ml for 20 h were irradiated with 60Co gamma-ray, fast neutron or thermal neutron. The absorbed dose of the cells from thermal neutron was calculated by Kobayashi's model. The D0 value of fast neutron was 1.07 Gy, and the D0S of thermal neutron radiation with or without preincubation of the cells with 10B1-BPA were 0.46 Gy or 0.67 Gy, respectively. The RBEs of fast neutron, thermal neutron beams, and neutron capture therapy relative to 60Co gamma-ray were calculated as 2.78, 4.18, and 6.15 at 0.1 surviving fraction, respectively. These results indicate radiologically that thermal neutron capture therapy using 10B1-BPA is an excellent radiation therapy for malignant melanoma.     

Sensitivity of SP cell line of melanoma B16 to low- and high-ionizing radiation

Cancer stem cells (CSC) found in multiple tumor types and cancer cell lines were shown to be more resistant to low-LET radiation in comparison to other cancer cells. Therefore, CSC are supposed to determine the long-term effect of cancer therapy. Research into the CSC sensitivity to high-LET radiation is of great interest because of the advances in hadron therapy. The aim of this investigation is to compare CSC and other cancer cell sensitivity to the low- (60Co gamma-rays) and high-LET (neutron) radiation. To identify CSC, we used the low cytometry-based side population (SP) technique based on the CSC capacity to produce the efflux of the vital dye Hoechst 33342. SP and non SP cells were sorted and exposed to gamma and neutron radiation at doses of 1-10 Gy and 0.1-4.7 Gy, correspondingly. We applied the colony-formation test to examine the SP and non SP survival rate after irradiation. It was shown that the sensitivity of SP to gamma-irradiation was lower than that of other cells: D0 average values (+/- SE) made up 2.3 +/- 0.3 Gy and 1.4 +/- 0.2 Gy, correspondingly (p = 0.047). The survival rate of SP and non SP did not differ after neutron irradiation. The values of relative biological effectiveness of neutron radiation relative to gamma-radiation at the D10 level were 2.6 for SP and 2.1 for other cells. The obtained results justify for the first time a high efficiency of application of neutrons in radiotherapy from the point of view of CSC elimination.     

Involvement of CRH receptors in urocortin-induced hyperthermia

The actions of individual corticotropin-releasing hormone (CRH) receptor (CRHR1 and CRHR2) were studied on the hyperthermia caused by urocortin 1, urocortin 2 and urocortin 3 in rats. Urocortin 1, urocortin 2 or urocortin 3 was injected into the lateral brain ventricle in conscious rats and the colon temperature was measured at different times following injection, up to 6h. In order to study the possible role of CRH receptors, the animals were treated with a urocortins together with the urocortin receptor inhibitors CRF 9-41, antalarmin and astressin 2B to influence the action of urocortins in initiating hyperthermia. Urocortin 1 at a dose of 2microg caused an increase in colon temperature, maximal action being observed in body temperature at 3h. CRH 9-41 and antalarmin, CRHR1 receptor antagonists, prevented the urocortin-induced increase in colon temperature while astressin 2B (CRHR2 receptor antagonist) was ineffective. Urocortin 2 at a dose of 2microg showed a byphasic action in increase in colon temperature having the first peak between 30 min and 1h and the second peak at 4h following treatment. CRF (9-41) and antalarmin was ineffective while astressin 2B fully blocked the action of urocortin 2. Urocortin 3 in a dose of lmicrog increased colon temperature; the maximal effect was observed at 2h. CRF (9-41) and antalarmin was ineffective while astressin 2B fully blocked the action of urocortin 3. The results demonstrated that urocortin 1, 2 or 3 when injected into the lateral brain ventricle caused increases in body temperature is mediated by urocortin receptors. The action of urocortin 1 is mediated by CRHR1 receptor, while in the action of urocortin 2 and urocortin 3 CRHR2 receptor is involved.     

An unusual radiation-induced G2 arrest in the zygote of the BALB/c mouse strain

Female mice of the BALB/c strain were superovulated, mated with males of the same strain, and irradiated with 1 Gy of X-rays at hourly intervals during the first cell cycle of the embryos. Two types of effects were found in the embryos, depending on the time of X-irradiation. When irradiation was delivered between 14 and 21 h after human chorionic gonadotrophin (hCG) injection, cultured two-cell embryos developed normally up to the morula stage, where a high mortality occurred. On the other hand, when irradiation was given between 17 and 24 h after hCG injection, a high proportion of the eggs was unable to cleave and remained blocked at the one-cell stage. Cytofluorometric analysis of the pronuclear DNA content of uncleaved zygotes showed that DNA synthesis was unaffected by X-irradiation, and that they were blocked in G2 phase of the first cell cycle. Similar studies on other strains, as well as reciprocal crosses between BALB/c and F1(female BALB/c X male C57 BLACK) mice showed that the 'one-cell block' is determined by the maternal genotype and results most probably from a direct action of X-rays on a radiosensitive cytoplasmic factor necessary for the first embryonic cell division, and appearing 17 h after hCG injection. A high proportion of blocked zygotes (30-40 per cent) recovered partially, cleaved with a delay of about 20 h, and died soon after, almost none of them being able to reach the blastocyst stage. At the time of maximum radiosensitivity, the LD50 for development up to the blastocyst stage was 0.95 Gy.     

Cell cycle alteration, apoptosis and response of leukemic cell lines to gamma radiation with high- and low-dose rate

The aim of this work was to compare the effect of gamma radiation with sub-low dose-rate 1.8 mGy/min (SLDR), low dose-rate 3.9 mGy/min (LDR) and high dose-rate 0.6 Gy/min (HDR) on human leukemic cell lines with differing p53 status (HL-60, p53 deficient and MOLT-4, p53 wild) and to elucidate the importance of G2/M phase cell cycle arrest during irradiation. Radiosensitivity of HL-60 and MOLT-4 cells was determined by test of clonogenity. Decrease of dose-rate had no effect on radiosensitivity of MOLT-4 cells (D(0) for HDR 0.87 Gy, for LDR 0.78 Gy and for SLDR 0.70 Gy). In contrast, a significant increase of radioresistance after LDR irradiation was observed for p53 negative HL-60 cells (D(0) for HDR 2.20 Gy and for LDR 3.74 Gy). After an additional decrease of dose-rate (SLDR) D(0) value (2.92 Gy) was not significantly different from HDR irradiation. Considering the fact that during HDR the cells are irradiated in all phases of the cell cycle and during LDR mainly in the G2 phase, we have been unable to prove that the G2 phase is the most radiosensitive phase of the cell cycle of HL-60 cells. On the contrary, irradiation of cells in this phase induced damage reparation and increased radioresistance. When the dose-rate was lowered, approximately to 1.8 mGy/min, an opposite effect was detected, i.e. D(0) value decreased to 2.9 Gy. We have proved that during SLDR at first (dose up to 2.5 Gy) the cells accumulated in G2 phase, but then they entered mitosis or, if the cell damage was not sufficiently repaired, the cells entered apoptosis. The entry into mitosis has a radiosensibilizing effect.     

Modification of radiation damage in the canine kidney by hyperthermia: a histologic and functional study

The purpose of this study was to evaluate the effect of hyperthermia on the histologic and functional response of the canine kidney, a late-responding normal tissue, to irradiation. Both kidneys were irradiated. Radiation was delivered in single doses of 0, 10, or 15 Gy. Whole-body hyperthermia was used to produce renal kidney temperatures approximating 42.0 degrees C for 60 min. Thirty-six beagles were placed randomly in the following six treatment groups: control, whole-body hyperthermia alone, 10 Gy alone, 10 Gy + whole-body hyperthermia, 15 Gy alone, and 15 Gy + whole-body hyperthermia. Renal histologic and functional changes were assessed at 1 to 9 months after therapy. No changes were seen in glomerular filtration rate or renal tissue volumes in control or hyperthermia alone groups. Renal vascular and glomerular volumes were not affected significantly by any combination of hyperthermia and/or radiation. In all groups receiving radiation, glomerular filtration rate decreased, percentage renal tubular volume decreased, and interstitial volume increased significantly after therapy. The magnitude of these changes in the functional and histologic response of the kidney and the latent period before expression of this damage were dependent on radiation dose. However, hyperthermia did not modify expression of radiation damage in the kidney based on glomerular filtration rate and histologic quantification of renal tissue components.     

Monte Carlo simulation of neutron dose equivalent by photoneutron production inside the primary barriers of a radiotherapy vault

PurposeTo evaluate the neutron dose equivalent produced by photoneutrons inside the primary barriers of a radiotherapy vault.MethodsMonte Carlo simulations were performed for investigating the production of photoneutrons as well as neutron shielding requirements. Two photon beams of 15 and 18 MV struck sheets of steel and lead, and the neutron doses were calculated at the isocenter (P_iso) and at a distance of 50 cm from the inside wall (P_wall) while delivering 1 Gy to the patient. The proper thicknesses of borated polyethylene (BPE) and concrete were simulated to reduce neutron contamination.ResultsWhen the primary barrier consisted of a concrete alone, the neutron doses at P_iso were 0.5 μSv/Gy and 12.8 μSv/Gy for 15- and 18-MV, respectively. At P_wall, the neutron doses were 15.8 μSv/Gy and 318.4 μSv/Gy for 15- and 18-MV, respectively. When 15 MV photons interacted with metal sheets, the neutron doses were 0.4–22.2 μSv/Gy at P_iso and 15.8–812.5 μSv/Gy at P_wall, depending on the thickness and material of the metal sheets and neutron shielding. In the case of 18 MV photons with the same configuration, the neutron doses were 0.9–59.5 μSv/Gy and 73.9–5006.1 μSv/Gy for P_iso and P_wall, respectively. The neutron dose delivered to the patient was reduced to the level of the dose delivered with a concrete barrier by including a 10-cm-thick BPE for each beam.ConclusionsWhen the primary barrier shielding is designed with a metal sheet inside for high energy, proper neutron shielding should be constructed to avoid undesirable photoneutron dose.     

Risk estimation for fast neutrons with regard to solid cancer.

In the absence of epidemiological information on the effects of neutrons, their cancer mortality risk coefficient is currently taken as the product of two low-dose extrapolations: the nominal risk coefficient for photons and the presumed maximum relative biological effectiveness of neutrons. This approach is unnecessary. Since linearity in dose is assumed for neutrons at low to moderate effect levels, the risk coefficient can be derived in terms of the excess risk from epidemiological observations at an intermediate dose of gamma rays and an assumed value, R(1), of the neutron RBE relative to this reference dose of gamma rays. Application of this procedure to the A-bomb data requires accounting for the effect of the neutron dose component, which, according to the current dosimetry system, DS86, amounts on average to 11 mGy in the two cities at a total dose of 1 Gy. With R(1) tentatively set to 20 or 50, it is concluded that the neutrons have caused 18% or 35%, respectively, of the total effect at 1 Gy. The excess relative risk (ERR) for neutrons then lies between 8 per Gy and 16 per Gy. Translating these values into risk coefficients in terms of the effective dose, E, requires accounting for the gamma-ray component produced by the neutron field in the human body, which will require a separate analysis. The risk estimate for neutrons will remain essentially unaffected by the current reassessment of the neutron doses in Hiroshima, because the doses are unlikely to change much at the reference dose of 1 Gy.